The present invention relates to a high-brightness diffusion plate applied to a direct-type backlight module whose surface is disposed with a plurality of trapezoid lens. By the trapezoid lens, the direct-type backlight module provides better output light with higher brightness and uniform diffusion.
During various kinds of flat panel displays, liquid crystal displays have received heightened research and development attention. Due to manufactures in Japan, Korea and Taiwan that are investing heavily in the research and development of this field and using more large-scale factory equipment for manufacturing, the quality of LCD display is improved with lower cost so that the needs for the display are increased. For satisfying more requirements of the LCD, the main trends of LCD include: (1) Increased area of glass substrate and continuous development among generations of LCD production from the seventh generation factory to the eighth, even the ninth generation factory. (2) New technology for color filter such as molding process that reduces the cost or the roller to roller process that breaks bottlenecks of manufacturing processes. (3) integration of the polarizing plate with the retardation film and the traditional casting process is replaced by an extrusion process. (4) New technology for light sources and optical films that makes external electrode fluorescent lamp and flat light source more feasible and practical and LED is used as main light source for backlight module. (5) Technology for integrating the diffusion film with the prism sheets. In the present invention, the diffusion plate is integrated with the prism sheets (brightness enhancement film).
The electric filed is necessary for liquid crystal displays to pull or align the liquid crystal molecules and the liquid crystal displays is illuminated from the back by a backlight module. Generally, backlight modules of liquid crystal displays are divided into two major categories according to numbers of lamps 10 and positions of light diffusion component 12: edge light type and direct-type. As shown in FIG. 1A, the edge light type backlight module can't provide high brightness and uniform light when being applied to large screen LCD displays due to number of the lamps 10 and light transmitting distance. Refer to FIG. 1B, the direct-type backlight module meets requirements of high intensity and uniform diffusion of light by increasing of the lamp 10 number and better design of diffusion component.
Refer to FIG. 2, a conventional direct-type backlight module consists of a reflector 20, a cold cathode fluorescent lamp (CCFL) 22 as a light source, a diffusion plate 24, a lower diffuser sheet 26, a prism sheet 28 and an upper diffuser sheet 30, from bottom to top sequentially. The backlight module connects with a liquid crystal display panel 32. Both the LCD screens and notebooks are edge lighting and only a personal user uses the device in short distance, the horizontal viewing angle is no longer important. Thus by light guide plate in combination with two mutually perpendicular prism sheets 28, light energy over 45 degrees is focused on a central point so as to enhance brightness. However, on LCD televisions, it's common to have a plurality of viewers at the same time so that the horizontal viewing angle matters. Generally during direct-type backlight module, a brightness enhancement film is formed by a diffusion plate together with the prism sheet 28 and the brightness enhancement film is used in combination with top and bottom diffusion films as a light diffusion element.
Take A direct-type backlight module for a 32″ liquid crystal display television as an example, cost for key components is as following: prism sheet accounts for 38%, diffusion film for 5% and the diffusion plate for 10%. Thus the most expensive component is the backlight module is the prism sheet and the cost is dramatically reduced without the prism sheet.
Therefore, the present invention provides a diffusion plate with trapezoid microstructure that is applied to diffusion plates of direct type backlight modules for brightness enhancement and uniformness. Moreover, the prism sheet can be omitted for saving cost and the device is easy to be mass-produced.